Nanoclusters of Lipid-anchored Proteins in Membranes: How and where do they form? Abstract Recent studies have shown that lipid-anchored signaling proteins dynamically organize into nanoscale substructures on the plasma membrane. The resulting protein-lipid nanoclusters serve as hubs for high-fidelity signal transmission. However, the molecular basis of how nanoclusters form and distribute in heterogeneous membrane domains remains undetermined. As a result, it is unclear how nanoclusters of homologous proteins, such as the signaling switches H-ras and K-ras, segregate to different lipid domains. We hypothesize that this would be achieved by a combination of lipid-based and protein-based sorting mechanisms. We plan to test this hypothesis using multi-scale molecular simulations and theoretical approaches complemented by collaborative experiments. We will use the H- and K-ras oncoproteins as model systems. Ras nanoclusters have intriguing implications for unique mechanisms of signal regulation at the plasma membrane. Elucidating the mechanisms that drive the spatiotemporal organization of Ras nanoclusters will therefore lead to a better understanding of cell signaling. In addition, whil this proposal is focused on Ras, the approach and principles that are developed will be applicable for the study of any lipidated signaling protein. The broader impacts of the work include contributions to potential therapeutic strategies for targeting Ras nanodomains and the biophysics of coupled protein/lipid sorting.